Well-Defined Heterobimetallic Reactivity at Unsupported Ruthenium-Indium Bonds

Bimetallic neutral and anionic complexes of transition metal (Co, Mn) carbonyls with indium(III) phthalocyanine

Heterobimetallic {[Co(CO)4]-[InIII(Pc2-)]} (1) and (Cp*2Cr+){[Mn(CO)5]-[InIII(Pc˙3-)]}·2C6H4Cl2 (2) complexes based on indium(III) phthalocyanine (Pc) were obtained as crystals. The complexes were synthesized by single (1) and double (2) reduction of indium(III) phthalocyanine chloride in the presence of transition metal carbonyls. Complex 1 contains dianionic Pc2- macrocycles. Thus, the coordinated Co(CO)4 carbonyl accepts an electron in the one-electron reduction forming a diamagnetic [Co(CO)4]- anion. Complex 2 contains a heterobimetallic {[Mn(CO)5]-[InIII(Pc˙3-)]}- anion and paramagnetic Cp*2Cr+ counter cations. Therefore, in the double reduction, electrons are transferred to Mn(CO)5 forming a diamagnetic [Mn(CO)5]- anion and to the Pc2- macrocycle forming a paramagnetic radical Pc˙3- trianion. Such assignments for 1 and 2 are in line with optical spectra, crystal structures and the data of magnetic measurements. The spectrum of 1 in the UV-visible range is similar to that of the starting InIIIClPc. The formation of 2 is accompanied by an essential blue-shift of the Q-band of Pc as well as by the appearance of an intense NIR band at 1005 nm characteristic of Pc˙3-. Compound 1 is EPR silent and diamagnetic, whereas the value of the effective magnetic moment of 2 is 4.24μB at 300 K, which corresponds to the contribution of S = 1/2 (Pc˙3-) and S = 3/2 (Cp*2Cr+) spins. Both weakly coupled paramagnetic centers (J = -0.41 cm-1) are observed in the EPR spectra.

Zinc-Promoted ZnMe/ZnPh Exchange in Eight-Coordinate [Ru(PPh3 )2 (ZnMe)4 H2 ]

The syntheses, reactivity and electronic structure analyses of [Ru(PPh₃)₂(ZnMe)₄H₂], 1 a, and [Ru(PPh₃)₂(ZnPh)₄H₂], 2 b, are reported. 1 a exhibits an 8‐coordinate Ru centre with axial phosphines and a symmetrical (2 : 2) arrangement of ZnMe ligands in the equatorial plane. The ZnMe ligands in 1 a undergo facile, sequential exchange with ZnPh₂ to give 2 b, which shows a 3 : 1 arrangement of ZnPh ligands. Both 1 a and 2 b exist in equilibrium with their respective 3 : 1 and 2 : 2 isomers. Mechanisms for ZnMe/ZnPh exchange and isomerisation are proposed using DFT calculations. The relationships of these {Ru(ZnR)₄H₂} species to isoelectronic Group 8 transition metal polyhydrides and related Schlenk equilibria in the Negishi reaction are discussed.

Bonding and Reactivity of a Pair of Neutral and Cationic Heterobimetallic RuZn2 Complexes

A combined experimental and computational study of the structure and reactivity of two [RuZn2Me2] complexes, neutral [Ru(PPh3)(Ph2PC6H4)2(ZnMe)2] (2) and cationic [Ru(PPh3)2(Ph2PC6H4)(ZnMe)2][BArF4] ([BArF4] = [B{3,5-(CF3)2C6H3}4]) (3), is presented. Structural and computational analyses indicate these complexes are best formulated as containing discrete ZnMe ligands in which direct Ru-Zn bonding is complemented by weaker Zn···Zn interactions. The latter are stronger in 2, and both complexes exhibit an additional Zn···Caryl interaction with a cyclometalated phosphine ligand, this being stronger in 3. Both 2 and 3 show diverse reactivity under thermolysis and with Lewis bases (PnBu3, PCy3, and IMes). With 3, all three Lewis bases result in the loss of [ZnMe]+. In contrast, 2 undergoes PPh3 substitution with PnBu3, but with IMes, loss of ZnMe2 occurs to form [Ru(PPh3)(C6H4PPh2)(C6H4PPhC6H4Zn(IMes))H] (7). The reaction of 3 with H2 affords the cationic trihydride complex [Ru(PPh3)2(ZnMe)2(H)3][BArF4] (12). Computational analyses indicate that both 12 and 7 feature bridging hydrides that are biased toward Ru over Zn.

Zn-Promoted C-H Reductive Elimination and H2 Activation via a Dual Unsaturated Heterobimetallic Ru-Zn Intermediate

Reaction of [Ru(PPh₃)₃HCl] with LiCH₂TMS, MgMe₂, and ZnMe₂ proceeds with chloride abstraction and alkane elimination to form the bis-cyclometalated derivatives [Ru(PPh₃)(C₆H₄PPh₂)₂H][M′] where [M′] = [Li(THF)₂]⁺ (1), [MgMe(THF)₂]⁺ (3), and [ZnMe]⁺ (4), respectively. In the presence of 12-crown-4, the reaction with LiCH₂TMS yields [Ru(PPh₃)(C₆H₄PPh₂)₂H][Li(12-crown-4)₂] (2). These four complexes demonstrate increasing interaction between M′ and the hydride ligand in the [Ru(PPh₃)(C₆H₄PPh₂)₂H]⁻ anion following the trend 2 (no interaction) < 1 < 3 < 4 both in the solid-state and solution. Zn species 4 is present as three isomers in solution including square-pyramidal [Ru(PPh₃)₂(C₆H₄PPh₂)(ZnMe)] (5), that is formed via C–H reductive elimination and features unsaturated Ru and Zn centers and an axial Z-type [ZnMe]⁺ ligand. A [ZnMe]⁺ adduct of 5, [Ru(PPh₃)₂(C₆H₄PPh₂)(ZnMe)₂][BAr^F₄] (6) can be trapped and structurally characterized. 4 reacts with H₂ at −40 °C to form [Ru(PPh₃)₃(H)₃(ZnMe)], 8-Zn, and contrasts the analogous reactions of 1, 2, and 3 that all require heating to 60 °C. This marked difference in reactivity reflects the ability of Zn to promote a rate-limiting C–H reductive elimination step, and calculations attribute this to a significant stabilization of 5 via Ru → Zn donation. 4 therefore acts as a latent source of 5 and this operational “dual unsaturation” highlights the ability of Zn to promote reductive elimination in these heterobimetallic systems. Calculations also highlight the ability of the heterobimetallic systems to stabilize developing protic character of the transferring hydrogen in the rate-limiting C–H reductive elimination transition states.

Transforming PPh3 into bidentate phosphine ligands at Ru-Zn heterobimetallic complexes

The reaction of [Ru(PPh₃)₃Cl₂] with excess ZnMe₂ led to P-C/C-H bond activation and P-C/C-C bond formation to generate a chelating diphenylphosphinobenzene ligand as well as a cyclometallated (diphenylphosphino)biphenyl group in the final product of the reaction, [Ru(dppbz)(PPh₂(biphenyl)')(ZnMe)] (1; dppbz = 1,2-bis(diphenylphosphino)benzene); PPh₂(biphenyl)' = cyclometallated PPh₂(biphenyl). The mechanism of reaction was studied and C-C coupling to give a bidentate 2,2'-bis(diphenylphosphino)biphenyl (BIPHEP) ligand was suggested to be one of the key steps of the process. This was confirmed by the reaction of [Ru(BIPHEP)(PPh₃)HCl] with ZnMe₂, which also gave 1. An analogous set of steps took place upon addition of ZnMe₂ to [Ru(rac-BINAP)(PPh₃)HCl] (rac-BINAP = racemic(2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) to give [Ru(dppbz)(PPh₂(binaphthyl)')ZnMe] (3). H₂ and the C-H bond of PhC[triple bond, length as m-dash]CH added across the Ru-Zn bond of 1, and also reversed the phosphine cyclometallation, to give [Ru(dppbz)(Ph₂P(biphenyl))(H)₂(H)(ZnMe)] (4) and [Ru(dppbz)(Ph₂P(biphenyl))(C[triple bond, length as m-dash]CPh)₂(H)(ZnMe)] (5) respectively.

Heterobimetallic ruthenium–zinc complexes with bulky N-heterocyclic carbenes: syntheses, structures and reactivity

Addition of ZnMe₂ to cationic and neutral ruthenium hydride complexes bearing NHC ligands affords new Ru–Zn heterobimetallic complexes.